1. Field of the Invention
The present invention relates generally to technology and business solutions directed to the correction of ophthalmic defects. In particular, the invention describes systems, instructions, and methods directed to providing a predictive outcome for therapeutic ophthalmic correction of vision disorders. The invention is intended to provide a higher degree of patient vision quality resulting from vision correction procedures.
2. Description of Related Art
A large percentage of the population have vision defects that are commonly referred to as myopia (near-sightedness) and hyperopia (far-sightedness), sometimes with an accompanying defect know as astigmatism. Myopia and hyperopia are the result of a lower-order optical aberration called defocus. Simple astigmatism is also a lower-order aberration. Briefly, a perfectly myopic eye brings all incoming parallel light to a focal point in front of the retina; a perfectly hyperopic eye brings all incoming parallel light to a focal point behind the retina; and a simply astigmatic eye focuses some of the light in a horizontal line and some of the light in a vertical line at some separation distances from the retina.
For a long time, practitioners have attempted to accurately measure these defects and correct them with spectacles, contact lenses, and other devices and/or procedures. Popular therapeutic procedures were, and continue to be, developed that use a suitable laser beam (typically, an excimer laser having a wavelength of 193 nm) to photoablate volumetric portions of an exposed corneal surface, thus modifying the shape of the cornea to refocus the incoming light. Photorefractive keratotomy (PRK), laser in-situ keratomileusis (LASIK), and laser epithelial keratomileusis (LASEK) are examples of photoablative refractive surgeries to correct the optical defects mentioned above.
We can now also accurately measure what are known as higher-order optical aberrations with advanced diagnostic technology such as, e.g., a wavefront sensor. These higher-order aberrations come from defects within the overall optical system of the eye (not just a misshapen corneal surface) and contribute to poor vision quality by reducing acuity and/or contrast sensitivity, causing glare, poor low-light vision, and in other ways. Not surprisingly, device manufacturers and practitioners have responded with techniques, instrumentation and devices, and therapeutic procedures that attempt to correct vision to the theoretical limit of 20/8 (known as supervision) or, practically, to optimize vision quality by eliminating, minimizing, or balancing these aberrations, or otherwise directing their attention to the higher-order defects.
For a variety of known and yet undiscovered reasons, the intended results of customized photoablative refractive surgery and customized lens applications including contacts, inlays, onlays, and IOL′', for example, have been elusive. Investigators have focused on the structure and physiology, and sophisticated modeling, of the eye to better understand the dynamics of correcting vision defects. The interested reader is directed to an article by Cynthia Roberts, Ph.D., The cornea is not apiece of plastic, Jour. Ref. Surg., 16, pp 407–413 (July/August 2000). Dr. Roberts hypothesized that if the cornea were similar to a homogeneous piece of plastic, a procedure known as radial keratotomy (RK) would not have worked because a biomechanical response to the structure altering incisions would not have occurred. (RK is a surgical procedure designed to correct nearsightedness by flattening the cornea with a series of incisions that resemble the spokes of a wheel). There is an increasing confidence among persons skilled in the art of refractive vision correction that the biomechanics (the biodynamic response of the eye to an invasive stimulus) of the eye, specifically of the cornea, significantly affects the outcomes of laser vision correction. Roberts, id, reports changes in anterior corneal geometry due merely to the keratectomy (flap cut) prior to laser ablation. The biomechanical corneal response to an invasive stimulus such as a keratectomy prior to LASIK or the severing of corneal lamellae by the laser in a PRK procedure can be explained, according to Roberts, by conceiving the cornea not as a piece of plastic, but rather as a series of stacked rubber bands (lamellae) with sponges between each layer (interlamellar spaces filled with extracellular matrix). The rubber bands are hypothesized to be in tension, since there is intraocular pressure pushing on them from underneath, and the ends are held tightly by the limbus. The water content of each sponge depends upon how each rubber band is stretched. Greater tension squeezes more water out of the sponges so the interlamellar spacing decreases; i.e., the cornea gets flatter. Thus the act of laser surgery itself to reshape the cornea may alter the corneal bio-structure with the effect that what you see is not what you get. U.S. Patent Application Publication 2002/0103479A1 to Sarver discusses optimizing the predictability of a vision correction method using surgical outcomes in an iterative analysis to create an optimized treatment outcome. Published PCT application WO 00/45759 discusses the interaction between the photoablative laser system used and the wound healing response of the eye and concludes that correction factors (“fudge factors”) in the range of ±1000× must be inserted in the sum of Zernike coefficients and Zernike polynomials to account for the eye's healing response. Published U.S. patent application Ser. No. US 2002/0007176A1 discusses a radially dependent ablation efficiency in the form of a modifying polynomial based on the optical path difference between a plane wave and a measured wavefront from a patient's eye. In many instances, surgeons will modify the manufactures' treatment profiles by their personal nomograms, which typically only provide a power shift correction. This type of personal modification, however, is generally based upon a relatively small sample of patients and procedures, thus general applicability and optimization may not be achieved. U.S. Pat. No. 5,891,131 entitled “Method and Apparatus for Automated Simulation and Design of Corneal Refractive Procedures” describes a computerized finite element method for simulating patient-specific corneal deformation in response to corneal incisions and/or corneal ablation procedures. The patent provides a general framework for this type of approach but does not appear to have solved the problem of optimized predictive analysis. A comprehensive review of finite element methods for simulating refractive surgical procedures on the human cornea is set forth in a 1994 dissertation by Datye which concludes that further work needs to refine the analysis and include other effects and phenomena which may be important in corneal modeling. All of these efforts highlight the attempts by manufacturers and practitioners to modify and customize ablation algorithms or nomograms to more accurately predict and achieve desired refractive outcomes. It is apparent, however, that the puzzle representing perfect vision, supervision, emmetropia, or optimum vision quality, by whatever name, still has missing pieces. For example, induced spherical aberration and other higher-order aberrations are known conventional post-LASIK effects that cause residual vision defects and sub-optimum visual quality. However, the cause and elimination of these treatment induced aberrations continue to challenge manufacturers and practitioners alike.
In view of the aforementioned developments, the inventors have recognized a need for hardware, software, and methods that will facilitate optimum outcomes of therapeutic ophthalmic procedures, in particular, photoablative refractive vision correction and, alternatively, customized ophthalmic optics, that result in optimum vision quality and greater patient satisfaction.